1. Field of the Invention
The present invention relates in general to methods and apparatuses for forming high pressure seals between two wellbore members, e.g., casing members operable in wells for the recovery of hydrocarbons or other minerals. More specifically, the invention relates to an annular sealing assembly that includes ridges and grooves called “wickers,” which are arranged to provide both an effective sealing engagement with adjacent wellbore members and an axial restraint of the wellbore members.
2. Description of the Related Art
In an oil or gas well, a wellhead will generally be located on the ground surface or on the sea floor for a subsea well. The wellhead is generally a tubular member having an axial bore through which other wellbore members may extend. For instance, a casing hanger often extends through the wellhead to support a casing string that extends below the wellhead into the well. A casing hanger is usually supported on at least one load shoulder within the axial bore such that an annular pocket is defined between the casing hanger and the wellhead. An annular sealing assembly may be provided within the annular pocket, e.g., to contain internal well pressure.
There are many types of annular sealing assemblies. Many of these sealing assemblies include sealing bodies constructed of rubber, other elastomeric materials, or metallic components. One type of seal body for creating a metal-to-metal seal has a u-shaped cross-section defined by inner and outer legs. The inner and outer legs are radially separated from one another and coupled to one another at their lower ends. An energizing ring is pressed downwardly into an annular clearance between the inner and outer legs to force the legs apart, and thereby force the legs into sealing engagement with adjacent wellbore members. The adjacent wellbore members may include, e.g., the wellhead and casing hanger.
Often the adjacent wellbore members include sealing surfaces for engaging the inner and/or outer legs, and often these sealing surfaces include wickers. Wickers are generally defined by adjacent ridges and valleys disposed in a generally parallel configuration. Wickers are generally distinguishable from threads, in which ridges and valleys may be disposed in helical pattern. When wickers are provided on both an exterior sealing surface of the casing hanger and on an interior sealing surface of the wellhead, the inner leg of the seal body embeds into the wickers of the casing hanger and the outer leg of the seal body embeds into the wickers of the wellhead. The legs of the seal body are often constructed of a metal that is softer than the wickers such that the wickers “bite” into the legs as the legs are embedded. The embedded legs effectuate a seal, and also perform a lockdown function, e.g., axially restraining the casing hanger within the wellhead.
The sealing and lockdown capacity of a sealing assembly can be affected by various factors. For instance, the relative hardness of the wickers with respect to the hardness of the seal body affects the degree to which the walls of the seal body embed into the wickers. Also fluids such as drilling mud, water, or wellbore fluid trapped in the grooves of wickers can lead to hydraulic lock, and frustrate the embedding of the walls. It is desirable to provide a high degree of both sealing and lockdown performance even when the embedding of the walls is frustrated.